You might want to consider using parts for outside yard lights made by a company called Malibu. They use press in bulbs rather than the screw in type. They are very inexpensive and you can work them off a low voltage transformer. Another option is to use miniture christmas tree lights. Their cost is almost nothing. You can pick up a string of 100 lights during the after christmas sales for about $1. You just take the strings apart and individually wire them in your buildings. You just twist the ends of the wires together for each side of the circuit. Cover with a small piece of electrical tape and they will last for a long time. If you use colored lights the blue, green, orange and red can give you some nice night time effects.
I would avoid screw in ones, bulbs tend to rust inside the sockets outside. Using some silicon dielectric grease might help to avoid that problem. Used it on my lighthouse bulb and it's done well ever since. Worked good on some connections on my old stereo also! Jerry